1. Field of the Invention
The present invention relates, in general, to a system and method for filling hydrodynamic bearings with fluid and, more particularly, to a system and method for filling hydrodynamic bearings with fluid, which can completely eliminate air bubbles from micro-gaps in the hydrodynamic bearings and prevent the infiltration of air bubbles in fluid charged in the bearings.
2. Description of the Related Art
Generally, hydrodynamic bearings are devices used in motors of Hard Disk Drives or CD-Drives. A hydrodynamic bearing includes a shaft and a sleeve, with viscous fluid, such as oil, charged in a micro-gap between the shaft and the sleeve to support free rotation of the shaft due to dynamic pressure formed in the fluid during rotation of the shaft relative to the sleeve.
To fill the micro-gap between the shaft and the sleeve of the hydrodynamic bearing with fluid, the fluid is charged in the bearing such that air bubbles are not formed in the fluid and surplus fluid does not remain around the bearing. However, filling such a bearing with fluid is very difficult, and requires a complicated procedure.
A conventional method for filling such hydrodynamic bearings with fluid is disclosed in Japanese Patent Laid-open Publication No. 2002-5170 and is shown in FIGS. 4A through 4D of the accompanying drawings.
To fill a hydrodynamic bearing with fluid according to the conventional fluid filling method, lubrication oil 25 is supplied into a gap between a shaft 2 and a plate 3, as shown in FIG. 4A. During the oil supply step, the bearing 1 is rotated at a low speed and, thereafter, the dispenser 4 comes into contact with the shaft 2 and then drips lubrication oil 25 onto an area around the inlet of the gap.
Thereafter, as shown in FIG. 4B, the bearing 1, onto which the lubrication oil 25 has been dripped, is inserted into a hermetic vacuum vessel 7 prior to exhausting air from the vacuum vessel 7 to the atmosphere using a vacuum pump, as shown by the arrow 6 in the drawing to place the vessel 7 in a vacuum state. In the above state, the surplus air remaining in the gap of the bearing 1 is removed from the bearing 1 in the form of air bubbles.
As shown in 4c, a throttle valve 24 is opened to supply air into the vacuum vessel 7 and allow the internal pressure of the vessel 7 to gradually return to atmospheric pressure. In the above state, the lubrication oil 25 is pressurized by the inlet air of the vacuum vessel 7, so that the oil 25 flows to the corners of the gap and is forced under pressure into the gap. Furthermore, after the lubrication oil 25 has been forced into the gap, the small quantity of air bubbles remaining in the lubrication oil 25 can be reduced by maintaining the temperature of the vacuum vessel 7 at 60° C. or higher.
Thereafter, as shown in FIG. 4D, while the bearing 1 is rotated at a low speed, the surplus lubrication oil 25 is sucked under reduced pressure from the gap of the bearing 1 using a pipe 14, as shown by the arrow 10 in the drawing.
However, the above-mentioned conventional fluid filling method is problematic in that the lubrication oil 25 must be charged under pressure into the gap without removing air from the gap of the bearing 1, so that the air cannot be completely removed from the gap and, furthermore, the air may be introduced into the lubrication oil 25 while the air is exhausted from the gap.
Furthermore, after the lubrication oil 25 has been forced under pressure into the gap of the bearing 1, the temperature of the vacuum vessel 7 must be maintained at a predetermined point or higher to remove remaining air bubbles, which complicates the fluid filling procedure.
Furthermore, when air is drained from the vacuum vessel 7 using the vacuum pump 6, the lubrication oil 25, which has been dripped on the bearing 1, may fly, thus contaminating the surroundings.